We currently have around 80,000 bloggers in our lists, but those lists are not used like traditional mailing lists, because of the constant new growth and attrition in the blogosphere.
With each new client, and each new outreach, we identify with the client what the demographic is they want to reach, then we ID the bloggers who are leading and influencing that demographic. We call these groups of bloggers that we identify as the group influencers a "universe".
The universes are built by rechecking the existing lists (adding newcomers and culling deadwood), and by building up brand new lists (since each client has a different set of demographics they want to reach.
We then reach out to these bloggers in a 4-6 week campaign which includes an initial semi-personalized outreach email, followed up by 2-4 follow-up emails. The emails are terse and the majority of the messaging is "outsourced" to a social media news release (SMNR - a one-page simple HTML microsite) that is a "steal me" sheet for the bloggers to make their blogging about our client super easy.
Each one of these outreach cycles generally leads to 100-300 social media mentions in blogs and on twitter (depending on how intriguing the client's message and offering is), invariably reaching millions and in many of our campaign's cases, 10MM+ people.
We integrate twitter campaigns (followership-building, messaging, and community engagement), Facebook, Youtube promotion, and A-list outreach as well. The most basic of our campaigns start at $10,000.